People hold posters as they gather in Trafalgar Square in central London to show their respect for the twelve people killed in Paris today in a terrorist attack at the headquarters of satirical publication "Charlie Hebdo" on January 7, 2015 (AFP Photo / Leon Neal) / AFP

London’s Trafalgar Square will host a vigil in solidarity with the victims of Wednesday’s Paris shootings in which 12 people were killed. Similar events are being held in other cities around the globe.